In continuous ink jet printing systems, the eyelid is a moveable seal which diverts ink on startup into the catcher, thereby recycling the ink while containing it within the printhead. The seal is formed against the lip of the metal catch plate, which is typically about 0.025 inches thick. The eyelid opens about 0.04 inches while the printer is printing, allowing the ink drops to pass onto the print media. The area behind the eyelid, containing the droplet generator and charging leads, is frequently accessed for cleaning over the life of a printhead.
The printhead is typically located over the top of a roller carrying the print media, with the ink drops moving downward in a roughly vertical direction. To assure good print quality, the printhead is 0.075 to 0.100 inches above the substrate. The eyelid must seal perpendicular to the drop path while not contacting the moving substrate on the roller. The motion paths of prior art have been limited to a linear sliding, or a single pivot. The linear paths of some prior art are guided by slots which are prone to collecting ink residue, leading to sticking or jamming of the eyelid.
Prior eyelids have used simple spring loaded solenoid actuators. The spring maintains the seal force until the solenoid opens it to a print position. However, the solenoid may create an excessive shock when the eyelid opens and impacts its print position stop. This shock jars the ink jet printhead, causing the printhead to malfunction. To prevent this, cushioning springs or rubber dampers are used to buffer the impact of the eyelid and solenoid plunger at the end of its travel.
Both the linear slide and the simple pivot eyelids are suitable for a seal moving a small distance from the sealed position to the print position. These configurations, however, do not move far enough to allow the operator to look at the jets and charging electrodes in a horizontal direction while they are cleaning the printhead. It is therefore necessary for the eyelid to be removed by a trained operator for printhead cleaning. This may entail removing screws and covers, necessitating the use of a tool for fasteners and the possibility that the parts may be lost or damaged on reassembly. Proper alignment of the sealing edge with the catchplate may be difficult to obtain after repeated disassembly, leading to leaks or poor startups.
An additional safety issue exists, since the printhead contains high voltage (.about.150 Volts). While operating, it is necessary to maintain proper ingress protection to avoid accidental contact with the charging electrodes. In the existing art the removal of covers by trained service personnel is the only means provided to prevent accidental access to the electrodes while the high voltage is on. With the cover removed, the eyelid may be removed, allowing accidental access to the high voltage during printhead operation. The system has no means to detect this operator override of the manufacturer's design or disable operation until it is corrected.
As mentioned earlier, it is possible for the eyelid to stuck or jammed. The prior art, with a simple solenoid actuator, has no feedback of eyelid position or presence. If the eyelid jams while closing, no indication is made to the system of the malfunction. This could result in ink spraying out of the printhead during start up or shut down.
In view of the weakness outlined in the prior art, it is therefore an object of the present invention to provide a means for sealing a printhead on startup, opening the seal to print, and opening further on an arbitrary path for cleaning. This is to be performed without the need for tools or removal of printhead parts.
It is another object of the present invention to provide such a seal means which minimizes mechanical shock as the seal and related parts move.
It is yet another object of the present invention to provide an interlock of the charge lead voltage to the eyelid position to protect the operator from electrical shock. The interlock is also designed to keep the high voltage off if the eyelid is removed from the printhead.
Finally, it is another object of the present invention to provide a means of feedback to the print station indicative of eyelid presence and position. Eyelid closure, proper print opening and service position are to be checked, allowing an eyelid malfunction to be detected.